1. Field of the Invention
The present invention relates to the microbiological industry, and specifically to a method for producing an L-amino acid using a bacterium of the Enterobacteriaceae family which has been modified to attenuate expression of the cpxR gene.
2. Brief Description of the Related Art
The cpxR gene encodes the CpxR protein, a member of the CpxR/CpxA two-component signal transduction system that senses a variety of envelope stresses, including misfolded proteins, and responds by upregulating periplasmic folding and trafficking factors. CpxR, the response regulator, mediates a response by activating transcription of stress-combative genes. CpxA resides in the inner membrane and has both kinase and phosphatase activities.
The expression of Cpx-regulated genes is induced during initial adhesion of Escherichia coli to abiotic surfaces, suggesting that the Cpx pathway plays a key role in the regulation of adhesion-induced gene expression (Otto, K. and Silhavy, T. J. Surface sensing and adhesion of Escherichia coli controlled by the Cpx-signaling pathway. Proc. Natl. Acad. Sci. U S A, 2002, 99(4):2287-2292). The surface-induced activity of the Cpx response requires NlpE, an outer membrane lipoprotein, which has been shown to induce the Cpx system when overproduced (DiGiuseppe, P. A. and Silhavy, T. J. Signal detection and target gene induction by the CpxRA two-component system. J. Bacteriol., 2003, 185(8):2432-2440).
The Cpx-mediated periplasmic stress response is subject to amplification and repression through positive and negative autofeedback mechanisms. Western blot and operon fusion analyses demonstrated that the cpxRA operon is autoactivated. Conditions that lead to elevated levels of phosphorylated CpxR cause a concomitant increase in transcription of cpxRA (Raivio, T. L., Popkin, D. L., and Silhavy, T. J. The Cpx envelope stress response is controlled by amplification and feedback inhibition. J. Bacteriol., 1999, 181(17):5263-5272).
Overproduction of the CpxR protein in Escherichia coli causes a drug resistance phenotype and affects transcription of genes involved in drug efflux (Hirakawa, H., Nishino, K., Hirata, T., and Yamaguchi, A. Comprehensive studies of drug resistance mediated by overexpression of response regulators of two-component signal transduction systems in Escherichia coli. J. Bacteriol., 2003, 185(6):1851-1856).
But currently, there have been no reports of inactivating the cpxR gene for the purpose of producing L-amino acids.